Scrubbers are widely used to neutralize or reduce the hazardous nature of hazardous materials and prevent their discharge into the environment. "Scrubbing" is a process whereby a gas or liquid is chemically reacted with another substance to produce a more safe and more easily handled product. Many types of scrubbers are known for performing this function. For example, packed and plate tower scrubbers are a very common type of scrubber for use in gas absorption. Other types of scrubbers include stirred tanks, sparged towers, spray towers, and falling-film absorbers.
Another type of scrubber, the venturi scrubber, is typically used in applications requiring particulate removal of hazardous material from a gas stream. Venturi scrubbers employ a concurrent flow of liquid and gas to remove material from the gas. These types of scrubbers are generally well known as is documented in a government report filed by Yung, Calvert, and Barbarika (NTIS, PB-271, 515, U.S. Dept. of Commerce, August, 1977).
Current venturi designs typically use one of three approaches: (1) a "wet approach" or "flooded-wall" entry section; (2) an adjustable throat venturi to accommodate pressure drops; or (3) a "flooded-elbow" located below the venturi. Another type of venturi-scrubber is disclosed in commonly owned U.S. Pat. No. 5,383,499. The scrubber described in the '499 Patent injects a gas stream into a reactor vessel fitted with baffles to increase reaction time. The units are best suited for gases which readily absorb or react with the scrubber liquid.
A simple scrubber unit is shown in prior art FIG. 1. FIG. 1 depicts a scrubber system 100 which comprises a container 10. A liquid treatment reagent is stored in container 10 and establishes a liquid level 24. Waste gas or liquid to be scrubbed is drawn into container 10 via inlet pipe 12 by a venturi eductor 14 disposed below liquid level 24 in container 10. The liquid treatment reagent and the waste gas or liquid react in venturi eductor 14 and in container 10 and the cleansed gas is released through an exhaust pipe 16 for further disposal. The motive force for venturi eductor 14 is generated by a flow of the liquid treatment reagent through reagent inlet pipe 18 from pump 20. Pump 20 draws liquid treatment reagent from container 10 via reagent withdrawal pipe 22. Under normal operating conditions, this system operates effectively to withdraw and scrub waste gas or liquids.
Such a scrubber, however, has the potential problem of "suckback." Suckback is a phenomena that occurs when liquid flow through venturi eductor 14 from pump 20 stops. Due to the vacuum conditions, the liquid in container 10 is sucked up into inlet pipe 12 and may be drawn back into the waste gas or liquid container. If the liquid enters a container which contains a product which is exothermically reactive, the uncontrolled reaction may produce catastrophic consequences.
One way to attempt to limit suckback is to place an automatic valve in stream with inlet pipe 12 to isolate the waste gas or reactor vessel from venturi eductor 14. The automatic valve senses the presence of liquid and closes down to isolate the liquid from the waste gas vessel. The automatic valve is not failsafe, however, and thus only limits the potential for suckback. Other drawbacks also exist.